Means for installing sleeves on hollow cylinders are known. These means consist of constructing and utilizing sleeves which are adjusted tight in relation to a support cylinder and which are installed on the aforementioned cylinder by generation of a film of air under pressure in the interface zone. For this purpose, the support cylinder is hollow and forms a closed chamber. Feeding air under pressure from this closed chamber is provided at one of the extremities while the nozzles, generally distributed in the direction of a generator, allow for the release of this air under pressure. Beginning with the coaxial casing of the sleeve, the first hole creates a film of air under pressure at the interface, radially dilates the sleeve, which, in the manner of an air cushion, permits the introduction of this sleeve over the entire length of the cylinder, if need be.
When the supply of compressed air is interrupted, the sleeve resumes its nominal diameter and the radial closing forces suffice to hold it in place, even in operation, i.e., during the rotation.
If this type of assembly is well known, a problem arises when it is necessary to install two sleeves on the same hollow cylinder in a superposed coaxial manner.
Flexographic and heliographic printing processes necessitate frequent changes of development between successive operations.
In arranging printing sleeves of various thicknesses for a given support cylinder one can cover a relatively significant spectrum of development for a single support cylinder.
These printing sleeves thus present some important economic advantages.
Nevertheless, for strong developments, it is necessary to use printing sleeves of significant thickness. These sleeves then become too heavy to be manipulated by a single operator for practical reasons as well as to adhere to load limits imposed by labor law. These sleeves can also have a very significant rigidity which can pose some assembly problems.
This is why intermediate or intercalary sleeves have been developed that are designed to be mounted on a support cylinder and to further support an exterior printing sleeve. These intermediate sleeves rest on the support cylinder. Only the outer sleeves are installed or dismounted.
In practice, the dimension of the intercalary sleeve is selected such that it can be associated with outer sleeves of relatively small thickness while being able to generate a spectrum of developments of relative significance.
Thus, only the outer sleeves are manipulated, their weight being quite inferior to that of the thick printing sleeves.
An intermediate sleeve can likewise be used in association with thin sleeves on which stereotypes for repeated use are permanently fixed. These thin sleeves are installed on the intermediate sleeve as a function of printing runs. This avoids turning to long mounting and dismounting operations of stereotypes on a printing sleeve. The risk of deterioration of stereotypes as well as the risk of errors during the positioning of stereotypes are likewise avoided.
Thus, if one has recourse to an intermediate or compensation sleeve, other problems arise when it is necessary to install a sleeve coaxially on another of the same nature. The coefficients of friction can turn out to be significant. Moreover, installation under pressure can only be conducted on the basis of a sole source of compressed air, namely the chamber constituted by the hollow cylinder.
A first problem which arises comes from the fact that the holes arc distributed along a generating line and are all open which engenders a poor pressure distribution. Indeed, if the first holes are plugged, the compressed air has a tendency to proceed on the other holes and to restrict the formation of a film of air between the sleeve and the cylinder. The limited pressure leads to a smaller radial dilation and to a rise in force. If the pressure is excessively increased, it risks damaging the sleeve at the end of installation when all the holes are closed which is not a satisfactory solution.
One can cite the document EP-0 732 201 which describes an intermediate sleeve of relatively significant thickness on which an outer sleeve can be installed in a relatively immovable manner.
Nevertheless, the assembly of the intermediate sleeve and the outer sleeve is not conducted directly on the support cylinder. Thus, after having installed the outer sleeve on the intermediate sleeve, it is still necessary to proceed to the installation of the group of two sleeves on the support cylinder. In this case, the presence of an intermediate sleeve does not permit lightening the overall weight of the piece which should be mounted on the support cylinder, and the intermediate sleeve does not resolve the problems of manipulation linked to the weight which have been mentioned above.
Document EP-0 711 665 describes an intercalary sleeve which is installed directly on a support cylinder, a thin outer sleeve being mounted immovably on the intermediate sleeve. Such an intermediate sleeve thus permits resolving the manipulation problems mentioned above.
Installing the outer sleeve on the intermediate sleeve is made possible as a result of a system comprising two bushings which are installed in the thickness of the intermediate sleeve on one extremity of this. One of the bushings is fixed in rotation in relation to the intermediate sleeve while the other bushing is free in rotation on the fixed bushing. These two bushings are pierced by radial conduits, those of the inner fixed bushing constantly being in communication with openings created in the support cylinder.
During assembly of the intermediate sleeve on the support cylinder, the mobile bushing is turned in relation to the fixed bushing such that their respective conduits do not coincide.
Thus, the air under pressure in the support cylinder can create a film of air which permits easy assembly of the intermediate sleeve on the cylinder. After installing the intermediate sleeve, the mobile bushing is turned in relation to the fixed bushing such that their respective conduits coincide. Thus, when air under pressure is injected into the support cylinder, a film of air is created on the outer surface of the of the intermediate sleeve which facilitates the installation of a thin outer sleeve on the intermediate sleeve.
Such a system effectively permits having available an intermediate sleeve on which thin outer sleeves selected as a function of the development required can be installed directly on the intermediate sleeve and the support cylinder.
Nevertheless, this system proves to be relatively complicated and onerous to operate. Moreover, the thickness of the intermediate sleeve should be sufficiently significant to permit accommodating the two bushings which limits its possibilities of use.
In the case of the installation of a compensation sleeve, another constraint is that the compensation sleeve should be blocked on the support cylinder after installation while allowing the posterior installation under pressure of the printing sleeve on this compensation sleeve.